1. Field of the Invention
The present invention relates to a solid state image pickup device for expanding the management range in the quantity of incident light in the high-luminance side and a method for driving the same, and in particular, to a solid state image pickup device for expanding the management range of the quantity of incident light for elevated luminances by setting up at least two signal charging periods in the specified period represented by the field or frame of a video signal and reproducing the signal charges in the signal charging period without using any external field memory or any frame memory and a method for driving the same.
2. Related Art of the Invention
According to a conventional technique, at least two mutually-different charging periods are set in one frame or one field in expanding the management range in quantity of incident light. For example, a first charging period T1 corresponding to the conventional vertical scanning period and a second charging period T2 shorter than the first charging period in the vertical blanking period are set in one field period TF. Then a signal charge Q1 obtained in the first charging period is reproduced with a gain of 1, and a signal charge Q2 obtained in the second charging period is reproduced with a gain (T1/T2). As a result, when the signal charge Q1 reaches a saturation charge quantity, a management range in quantity of incident light being (T1/T2) times greater than the gain in the conventional case is achieved by using the signal information of the signal charge Q2.
In the above-mentioned element drive method for expanding the management range in the quantity of incident light, there is a proposal for dispensing with any external frame memory (Japanese Patent Laid-Open Publication No. SHO 63-250980). The above-mentioned proposal describes a method for continuously transferring signal charges obtained in two charging periods separately provided in one field period TF in a vertical CCD by producing three signal packets with four pixels and a total of eight transfer electrodes according to the structure of the current CCD, using signal charges of a mixture of two pixels in the first charging period as two packets, and using signal charges of a mixture of four pixels in the second charging period as one packet.
However, it is required to read two times during a time interval of xcex94 T for the purpose of additively mixing the signal charges of the mixture of four pixels. There exist two different types of signal charges T2 and (T2 +xcex94 T) in an identical packet. When the signal charges of the mixture of four pixels in the two types of charging periods are mutually different in time by xcex94 T are subjected to calculation processing with the gain of (T1/T2) without distinction, there occurs disadvantages such as misalignment in color and misalignment in luminance when adjusting the second charging period T2 according to the quantity of light of the subject.
By using a drive method and solid state image pickup device free of the difference of xcex94 T between charging periods in the second charging period T2 that causes problems when signal charges are read from a photoelectric converting element to a vertical CCD at least two times in one field period, the management range in the quantity of incident light can be expanded. Therefore misalignment in color and misalignment in luminance can be avoided.
The management range in quantity of incident light can be expanded to the high-luminance side without using any external field memory or any frame memory for a subject having a wide range of distribution in luminance by managing the quantity of light smaller than a standard quantity of light and the quantity of light about two times greater than the standard quantity of light with the first charging period T1 and managing a region having a saturation charge quantity in the first charging period T1 with the second charging period T2 in the vertical blanking period.